Making integrated circuits generally includes using chemical mechanical polishing (CMP) for polishing and thereby planarizing one or more of the depositied layers necessary for making the integrated circuit. Polishing pads used in CMP, typically made of polyurethane, are expended in the CMP process after some number of uses. Thus, in the course of a year, for example, a large number of polishing pads may need to be acquired. Thus, the cost of the polishing pads is relevant to the cost of making integrated circuits. Further, polishing pads are difficult to make perfectly.
One common way that polishing pads are patterned is to use a cutting approach in which a polishing pad is made to spin and a sharp object is applied to the rotating pad, analogous to a lathe operation. This often results in small strips of polyurethane, called stringers, dangling from the polishing pad. The stringers are not easily removed and, as a practical matter in a commercial environment, may not be possible to completely remove. Thus, a reduced quality of polishing pad is tolerated in the integrated circuit manufacturing process.
Another technique for patterning a polishing pad is to use a laser. One of the disadvantages of a laser is that it is difficult to form grooves with vertical walls. The walls are relatively more sloped than from the lathe approach. Another disadvantage is the high amount of local heat generated at the point where the laser hits the polishing pad.
Another technique is to use a small rotating cutting device, analogous to a router, that cuts a pattern into the polishing pad. The advantage of this approach is that the pattern does not have to be concentric circles which has been the only practical pattern for the lathe approach. The router approach, however, requires a relatively long time to form a pattern that greatly increases cost and also may leave small stringers as well. Thus, the patterns that are considered desirable than the concentric circle pattern have not been found to be practical due to high cost.
Thus, there is a need for a technique to make polishing pads and the subsequent polishing using the polishing pads that overcomes or improves upon the existing techniques described above.